Such pumps are built, in general, with a pump chamber, in which liquid fuel is taken up and then ejected intermittently during the delivery operation. To generate the necessary vacuum to take up liquid fuel, as well as to eject fuel from the pump chamber, a piston may be moved to and fro, so that a defined volume of liquid is delivered during each stroke of the piston and the liquid to be delivered can thus be released in a correspondingly accurately metered quantity.